1. Field of the Invention
The present invention relates to a depth map generation method, in particular to a depth map generation method for producing a depth map belonging to an image signal so as to provide for use in an image conversion system for converting a two-dimensional planar image signal to a three-dimensional stereoscopic image signal.
2. Description of Related Art
The depth value of each image region contained in an image signal serves as an indispensable part for the functioning of a display device for presenting a stereoscopic image. Indeed, an erroneous depth value will result in seriously unfocused stereoscopic images, and subsequently such can bring discomfort to user's viewing experience. In further illustration, in order for a user to visually perceive a stereoscopic image, the user must first receive through his/her eyes' vision gradient, dynamics gradient, and other depth sensitive constituents, so as to obtain a relative object positioning relationship, and therefore to allow the user's brain to visualize a stereoscopic image.
Among these depth perception constituents, motion parallax turns to be the most controlling factor since it originates from the positive correlation between an object's motion amount and the distance between the object and object's observer. For instance, in a hypothetical situation involving two cars moving at the same speed and an observer, the car that is farther away from the observer will appear to move slower than the car that is closer to the observer, therefore the observer can determine the relative distance between the two cars using such observation. In addition to motion parallax, other important depth perception constituents such as linear perspective (the apparent merging of two parallel railway tracks seen in a remote distance), atmospheric perspective (the apparent visual obscuration of objects seen in a remote distance due to effect of small-size particles in the air), texture gradient (the apparent observation that the object in a remote distance appears more dense), elevation (the apparent observation that the object located at a greater height looks more distant), overlapping (the apparent observation of relative position between objects from the blocking between objects), and relative size (the apparent observation of identical objects in which the object located in a remote distance appears smaller, and the object located in a closer distance appears larger). These depth perception constituents have been converted to algorithms and applied in various types of 2D to 3D image/video transformation system.
However, the algorithms resulting from each of the aforementioned depth perception constituents has its disadvantages, some algorithms are only based on the apparent shape of the image region, while some other algorithms are only based on the size of the image region, and even some algorithms are only based on the color feature of the image region, resulting in the produced depth maps not satisfying the actual requirements. Furthermore, these algorithms cannot precisely provide depth values to each of the image regions that are of particular interest to the viewer, causing the viewer not being able to see stereoscopic images of the components that are interesting to the viewer and therefore minimizing the viewing pleasure.
Therefore, there is a demand in the industry for a depth map generation method for producing a depth map belonging to an image signal so as to provide for use in an image conversion system for converting a two-dimensional planar image signal to a three-dimensional stereoscopic image signal.